A polarizer used in a polarizing plate is an optical diode for converting natural light or any polarization into polarization in a specific direction, and is extensively used in a display device such as a liquid crystal display and an organic light emitting diode (OLED). Recently, as the polarizer used in the display device, a polyvinyl alcohol-based polarizing film where molecular chains containing an iodine-based compound or a dichromatic dye are aligned in a predetermined direction has been generally used.
The polyvinyl alcohol-based polarizing film is manufactured by a method of dyeing a polyvinyl alcohol-based film with an iodine or dichromatic dye and then performing stretching in a predetermined direction and cross-linking, and in this case, the stretching process may be performed by wet stretching performed in a solution such as a boric acid aqueous solution or an iodine aqueous solution, dry stretching performed under atmosphere, or the like. However, in an existing manufacturing process as described above, in order to perform stretching without occurrence of breakage, a thickness of the polyvinyl alcohol-based film before stretching needs to exceed 60 μm. This is because in the case where the thickness of the polyvinyl alcohol-based film before stretching is 60 μm or less, the degree of swelling of the polyvinyl alcohol-based film is increased and a modulus acted per unit area in the stretching process is increased due to the small thickness which easily causes breakage.
Meanwhile, in accordance with a recent trend of reducing a thickness of the display devices, the polarizing plate needs to have a smaller thickness. However, like the related art, in the case where the polyvinyl alcohol-based film having the thickness before stretching exceeding 60 μm is used, there is a limit in reducing the thickness of the polarizer. Accordingly, research for manufacturing the polarizer having a smaller thickness has been conducted.
Korean Patent Application Laid-Open No. 2010-0071998 discloses a method of manufacturing a thin polarizing plate by using a laminate manufactured by applying a hydrophilic polymer layer on a base material layer or co-extruding a base material layer forming material and a hydrophilic polymer layer forming material. However, in the case of the coating or co-extruding method, since it is not easy to separate a polyvinyl alcohol layer and the base material layer after stretching and high peel strength is required for separation, problems such as damage or deformation of the polyvinyl alcohol layer easily occur in a separation process, and as a result, an optical property such as the degree of polarization of the polyvinyl alcohol film is degraded. Further, in the case where the coating method or the co-extruding method is used, since the thin polarizing plate is manufactured by a method of melting a polyvinyl alcohol resin and then extruding the polyvinyl alcohol resin or manufacturing the polyvinyl alcohol resin in a coating liquid and then applying the polyvinyl alcohol resin, physical properties of the manufactured polyvinyl alcohol film are easily changed according to an extrusion condition, a coating condition, or a film manufacturing condition, and thus physical properties of the finally manufactured polyvinyl alcohol are degraded and it is difficult to implement uniform physical properties.
Accordingly, a thin polarizer having an excellent optical property needs to be manufactured.